Dental alloy and method of making same



Patented June 8, 1937 mm f STATES I I 2,083,052 I I DENTAL ALLOY ANDMETHOD OFMA'KING, I I SAMEI Edward L. Chott, Riverside, Ill." I

No Drawing. Application April 2,4;1935; I I Serial No. 17,931 I I 3Claimsp (Cl. 75-173) I his invention relates to an alloy adaptable Izinc which have been combined in carefully I worked out and definiterange of proportions This. alloy of my invention when finelycomminutedand triturated with the properproportionof mercury, results ina plastic mixture which will readily harden into a rigid metallic bodyin a relatively short time, and to a hardness r equal to that which willsustain apress ureconsiderably in excess of dental alloys preparedwithpresentlyrknown proportions and methods;

Most alloys used at present contain a large proportion oi silver anc lhave combined therewith a substantial amount ofcopper, it beingunderstood and assumed by makers of dental alloys that copper isanessential ingredient and used for I the pre s ently assumed essentialfunctionof limiting and stabilizingthe hardening of amalgam made withsuch a11oys..,It is also known that the coppercontent of dental alloysmaterially increases the discoloration and tarnishing of presently knownalloys due to reactions thereofwith the sulphur and other com- 0 poundscontained'in foods,

the use of copper and likewise eliminates its aforesaid lundesirablecharacteristics, at the same time; possessing'the same properties ofrelatively quick'hardening and lir'nitedbut desirable degree of"expansion anda hard tough resultant body which is free from cracks orpores. Various objects of my invention are set forth as -fol- I lows,

An' important object' of my invention is the r sure of approximately3,500 pounds per square I inch. 7

A further object of my invention is the provision of an alloy composedof proper proportions of silver, tin and zinc, and no copper whatever,which at the same time will not only have the desirable amount ofexpansion when setting, but which also has the important characteristicof I t I The alloy of my invention and its method of preparationeliminates at the same maintaining the natural'zcolorbf the alloy andnot susceptible to discoloration or tarnish when it has come in contactwith sulphur and other numerous agents presentin various foods.

A furt her important object of my invention is the provision of a dentalalloy for use in dental amalgams-which is composed of only silver, tin

and zinc in predetermined range of proportions and which has. astrongcharacteristic of maintaining its natural color as possessed by itbeforeactual use, namely, avoidingfltarnishland dis colorationTwhich. arecaused upon presently known dentalalloys containing silver by sulphur,and other agentsfound in .food andin the atmosphere in;the form ofgaseous "compounds.

Aiurther object of my invention is'the provision of' a n' alloy whichavoids "the conventional use of copper, copperbeing considered 'a s anecessary'j-ingredient of; presently known alloys, I copperfhavingundesirable characteristics of discolorationand tarnish and heretoforeconsidered asia stabilizer tovprevjentpver-expansion during setting andihardening, my said alloy being mixable with mercury to make a plasticmixture which will harden in a relatively short time to a degreemeasurable to withstand a pressure of approximately 3,500 pounds persquare inch, and which has a desirablefdegree ofex pansion on settingsuflicient to preventjleakage from within the tooth cavity intowhich theamalgam is inserted.

A further object of myinvention is the provi- I use in a novel dental'amalg'am which comprises melting the component metals in a sealed-furnace, thence pouring thejs'ame'into moulds; then dividing thesameinto fine particles by chipping, shaving and crushing and" thensealing and annealingthe same toprevent contraction or'over-' expansionwhen the amalgam made from such alloy is fully set and to control thehardening time thereof, such annealing being accomplished by placing thealloy in small containers under vacuum and boiling for desired periodsof time.

Another object of my invention is toovercome the undesirablecharacteristic brought about by the conventional use of copper,providing an alloy of finely divided particles which have been sieved orcrushed to a small size so that one troy ounce will measure from 8 to'10 cubic centimeters and which will yield an amalgam providing acomplete filling and sealing of the cavity without voids, cracks orchannels, either in the amalgam body or between it and the tooth.

It is well known by those familiar with ordinary sion of anovel process.of preparing an alloy for and presently known dental alloys that suchordinary alloys contain copper as a base ingredient, it being theassumption that the copper has the property of preventing over-expansionof the alloy upon setting and thereby acting as a stabilizer. Because ofthe general use of copper as a basic ingredient in presently knownalloys for making dental amalgam, all such alloys have the v undesirablecharacteristic of quickly becoming tarnished and discolored due to theaction of agents contained in foods, particularly sulphur, which in avery short time tarnishes the tooth filling to a dark and unnaturalappearance, usually a bluish gray color. lengthy and repeatedinvestigation that the use of copper can be entirely eliminatedproviding the proper proportions of the remaining ingredients specifiedhereinafter are combined in a manner and method which is novel in theart and which varies materially from presently known methods ofpreparing the dental alloy.

I first separate silver of a high degree of fineness (in a preferredproportion ranging from 71% to 78% of the total mass sought to beprepared) and melt the same in an electric or other suitable furnace,preferably of the induction type, so that during the melting process thealloy will be protected from contamination or oxidation. Tin of aproportion of from 21% to 28%, preferably 21.5% to 27.5%, and zinc of aproportion of less than one per cent and not less than 1., of one percent or any zinc proportion between of one per cent and 1%, is alsomelted in a suitable furnace in like manner and combined with the meltedsilver, whereafter I then pour the molten alloy into moulds, preferablyround bars or tubes, and allow the same to cool and harden. I have foundthat while any preparation of the three ingredients herein stated withinthe ranges aforesaid ishighly satisfactory, the most preferableproportions of tin is from 21.5% to 27% and of zinc from 1%- of one percent to and including 1%. Thereafter I cut the moulded bars or tubesinto fine chips or shavings, either in a lathe, milling or filingmachine. The resultant filings or shavings are then further reduced insize by sieving and crushing to a size so that from 8 to 10 cubiccentimeters thereof will weigh one troy ounce.

The next step in my method of preparing my dental alloy is the annealingthereof which imparts properties thereof to control the setting andhardening time to prevent contraction and excessive expansion after thealloy is set in the tooth cavity. The first step in my annealing processis to pour the sieved and crushed alloy of the desired fineness intoeither glass or preferably metal tubes, the bottom of which tubes havebeen sealed with an air-tight cap and the upper end of said tubepreferablyvhaving a screw capped I have found after fitting with a valvetherein. I then withdraw most of the air from each said tube by pumpingthe same out through aforesaid valve which will be closed against theentrance of air thereafter. I then place the tubes containing the alloyand in which partial vaccum is created into a tank of cold water, whichwater is slowly heated to the boiling point and left to boil for aninterval of time. If the size of the alloy particles contained in thetube is slightly larger than those which I I have specified in mypreferred example, the duration of the boiling of such water during saidannealing process should be proportionately longer. Further, theduration of the boiling time may also be gauged by the setting timerequired in order to obtain a fully annealed alloy which will retain itssize after slight expansion (ranging from 3 to 13 microns) when settingin a tooth cavity.

I am aware that numerous details of proportion may be varied through awide range without departing from the principles of this invention, andI therefore do not desire to limit the patent granted hereon otherwisethan necessitated by the prior art.

I claim as my invention:

1. A comminuted ternary alloy for dental amalgams composed of from 71%to 78% silver and from 21% to 28% tin and 1% zinc and which has and willmaintain its natural color and appearance, which will not have anexcessive amount of expansion on setting; and which is uncontaminateddue to maintenance thereof out of contact with the atmosphere during itsmelting, chipping, crushing and annealing steps.

2. An alloy for dental amalgams composed of from 72% to 78% silver andfrom 21.5% to 27.5%

' tin and fi% of one per cent to one per cent zinc,

in finely divided form and annealed and which has the desirablecharacteristics of maintaining its natural color and avoidingdiscoloration when placed in contact with food agents and gaseousatmospheric compounds, and which when triturated will form a hard bodyequal to a hardness capable of sustaining a pressure of 3,500 pounds persquare inch and which will not expand excessively or to great degree onsetting.

3. The method of preparing an alloy for dental amalgams which comprisesmelting from 72 to 78 parts of silver; 21 to 27 parts of tin and zinc offrom to one percent; thence casting the same into relatively smallmoulds; thence comminuting the same into relatively fine particles;thence placing the comminuted alloy into airtight containers; thenceexhausting most of the air from such containers and thence boiling saidcontainers and contained alloy in boiling water for a short interval oftime to anneal said contained alloy to the desired degree.

I EDWARD L. CHOTT.

